I really don't have any other suggestions, sorry.
I had a somewhat similar problem earlier this year (Device Manager indicated need for sound driver, but unable to install driver from motherboard CD)...and I wish I could take credit for solving it, but I can't. The problem went away alright, but I don't remember the exact steps I took.
I do know that I used that link to remove all sound drivers...and I think I followed up with running chkdsk /r (followed by reboot)...but I honestly can't say.
Anyway, good luck